The market for protein-based biopharmaceuticals is rapidly expanding. However, the clinical utility of many proteins is limited by their short serum half-life, requiring frequent injections. The most common approach to improve serum half-life is PEGylation. The chemical conjugation of Polyethylene glycol (PEG) to therapeutic proteins typically results in product mixtures that include inactive isomers and reduce the overall potency of the product. The chemical PEGylation of proteins significantly increases manufacturing costs, requiring precise process control and analytical assays to ensure reproducibility of product composition. The current project describes polypeptide chains (called rPEGs) that mimic the physicochemical properties of chemical PEG. rPEGs are hydrophilic and have very large hydrodynamic radii. Most importantly, rPEGs can be recombinantly fused to therapeutic proteins resulting in homogeneous products. The fusion of rPEGs to biopharmaceutical is expected to provide benefits that are similar to chemical PEGylation (long serum half-life, reduced immunogenicity) while offering improved product potency, homogeneity, and significantly reduced manufacturing costs. Phase I of this project was extremely successful and demonstrated the feasibility of the rPEG technology. rPEG sequences that closely mimic the properties of chemical PEG were developed. We demonstrated that a 20 kDa rPEG sequence has an apparent molecular weight of 180 kDa. Fusion of rPEG to the model protein GFP increased its serum half-life in rats from 1-3 h to approximately 10 h, similar to the effect of chemical PEGylation. Furthermore, this rPEG-GFP fusion elicited only a very weak immune response in rats. Our phase II goal is to apply rPEG technology to human growth hormone (hGH). hGH is currently used for the treatment of dwarfism in children. 2006 sales exceeded $3B. Due to its rapid plasma elimination, hGH treatment requires daily injections. No long-acting form of hGH has been approved and chemical PEGylation of hGH had limited success due to the formation of mixtures containing inactive isomers. We aim to develop methods for the production, purification, and formulation of rPEG-hGH. The resulting product will be thoroughly characterized in vitro and in vivo. The resulting data package will allow rPEG- hGH to enter clinical development. The methods and data developed during the project will validate rPEG technology and enable its broad application to other protein pharmaceuticals. PUBLIC HEALTH RELEVANCE: The utility of many biopharmaceuticals is limited by their short serum half-life, which requires frequent injections. The goal of this project is to develop recombinant peptide chains (called rPEG) that mimic the properties of polyethylene glycol. These rPEGs can be directly fused to protein pharmaceuticals to increase their serum half-life. We will validate rPEG technology by developing a long-acting version of human growth hormone for the treatment of dwarfism in children.